A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. including part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In order to monitor the lithographic process, it is desirable to measure parameters of the patterned substrate, for example the overlay error between successive layers formed in or on it. There are various techniques for making measurements of the microscopic structures formed in lithographic processes, including the use of scanning electron microscopes and various specialized tools. One form of specialized inspection tool is a scatterometer in which a beam of radiation is directed onto a target on the surface of the substrate and properties of the scattered or reflected beam are measured. By comparing the properties of the beam before and after it has been reflected or scattered by the substrate, the properties of the substrate can be determined. This can be done, for example, by comparing the reflected beam with data stored in a library of known measurements associated with known substrate properties. Two main types of scatterometer are known. Spectroscopic scatterometers direct a broadband radiation beam onto the substrate and measure the spectrum (intensity as a function of wavelength) of the radiation scattered into a particular narrow angular range. Angularly resolved scatterometers use a monochromatic radiation beam and measure the intensity of the scattered radiation as a function of angle.
During various processes within a lithography system, such as during inspection of a substrate by an inspection apparatus or during the transfer of a pattern to a substrate in a lithographic apparatus, as well as other processes that may be performed in a lithography system, a substrate may be supported on a substrate support or support structure. In order to be able to transfer the substrate from one part of a lithography system to another, for example in order to perform different processes, and in order to allow the substrates to be transferred into and out of the lithography system, it is desirable for the substrate to be loaded to and unloaded from the support structure. Accordingly, it has previously been known to provide a substrate support with one or more ejector pins which rise up from the substrate support, lifting the substrate away from the surface of the substrate support on which the substrate rests. During an unloading procedure, the substrate is lifted from the surface of the substrate support by the ejector pins. Once the substrate has been lifted, a substrate handler gripper or end-effector is inserted under the substrate, between the ejector pin(s), and is used to lift the substrate from the ejector pins. For a substrate loading process, the process is reversed.
It is desirable to operate lithography systems within carefully controlled environments. Accordingly, lithography systems are conventionally operated in so-called “clean rooms”. However, it will be appreciated that providing clean rooms having an appropriate level of air quality is costly. Accordingly, it is desirable to install as many lithography systems as possible within a given size of clean room. Therefore, it is desirable for lithography systems to be as compact as possible.